Image converter and amplifier



Aug- 13, 1963 G. R. RosENDAHL 3,100,817

' IMAGE CONVERTER AND AMPLIFIER Filed June 9. 1960 4 Sheets-Sheet 1 IN V EN TOR.

GOTTFR/ED R. ROSE/VDAHL Y Armi XVM/VM ATTORNEY Aug. 13, 1963 G. R. Rosi-:NDAHL 3,100,817.

IMAGE CONVERTER AND AMPLIFIER Filed. June 9, 1960 4 Sheets-Sheet 2 IN V EN TOR. GOTTFR/ED l?. ROSE/VDAHL BY 64,4% fue Mba/6% A 7' TORNE Y Aug. 13,4 1963 G. R. RosENDAHL 3,100,817

IMAGE CONVERTER AND AMPLIFIER l Filed June 9. 1960 4 Sheets-Sheet 3 Il 53 rm' 53 54 lM 54 5o sau eab 5| INVENTOR. GorrFR/ED R. RosEA/DAHL ATTR/VEY Aug. 13, 1963 G. R. Rosi-:NDAHL 3,100,317

IMAGE CONVERTER AND AMPLIFIER Filed June 9, 1960 4 Sheets-Sheet 4 LQ. a.

80 MIE H50.

` INVENTOR. F/ Z 60m-'m50 f?. Rosas/@AHL A T TORNE Y i 3,100,817 IMAGE CONVERTER AND AMPLIFIER Gottfried R. Rosendahl, Boulder, Colo., assignor to Ball Brothers Research Corporation, Boulder, Colo., a corporation of Colorado Filed June 9, 1960, Ser. No. 35,079 14 Claims. (Cl. )J8- 7.87)

This invention relates toirnprovements in an image converter and amplifier `and more particularly to a device for displaying, by optical projection, an image 'which is directly or indirectly produced by electrons, i.e., a device for converting an electron` image so as to be suitable for projection by visible light or similar radiation. The term directly produced electron image refers to an electron image which is directly produced on a sensitive surface of the converter. The term indirectly produced electron image refers to a uniform charge of electrons on a sensitive surface of `the converter `which is subsequently or simultaneously influenced by X-ray, Iultraviolet, or visible radiation, in such `a way that an electron image on the sensitive surface is obtained by re-emission of electrons, with a remaining but reversed intensity `distribution of electrons similar to an X-ray, ultraviolet, or visible light image on the sensitive surface.

A prior electron image converter has been used only for the conversion of directly produced electron images, such as produced in aTV picture tube by a scanning beam, into an optical image, which can be projected on a screen by `the help of a high power light source. Such a converter utilizes a relief produced on the surface of a special oil by an electronic beam, the oil covering the surface of a spherical ihirror in a thin layer. When the oil surface Vis chargedwith electrons, forces between the surface char-ges `and probably also between the surface charges and the mirror coating, deform the oil surface so that it then becomes `a relief. The relief is used to produce 'an optical displaythrougha special light system of the Schlieren type, which is limited to use with electron images produced by a scanning beam. Such a converter suffers several disadvantages. Thus, its Weight, volume, and sensitivity toward heavy vibrations prohibits its use in fast moving vehicles, such as rockets and satellites,

and makes its use diiiicult in air, ground and seagoing vehicles. Another disadvantage of such la converter is the time required for restoration of the original state, i.e., removal of the electron `charge and the relief on the oil surface, in order to prepare the surface for a change in the image. This diiculty has been partly overcome lby rotating the spherical mirror with the oil, to present a fresh oil surface and thereby gain time in which to restore the `used surface to its orifginal'state. `However, such a solution presents other diiiiculties, in that the movement of the spherical mirror with the oil must be very precise in order to maintain the optical arrangement. This impairs the possible ruggedness ofthe equipment and also increases the Iweight and volume of the device, as well as being quite costly. A further disadvantage of such a converter is the delicacy of the oil surface. 'I'he oil surface is directly 'exposed to the :electron beam,

which produces chemical changes in the oil which act as impurities to impair proper function, unless they are removed by some special process. Such a special process for removal of `such impurities again complicates the instrument and the adverse inuence of impurities also United States. arent hampers field use of the instrument under diflicult cont ditions, as fdr military purposes. A still 'further disadvantage is that the electron image `and optical image are fproduced from, or onfthe salme side of, theroil surface.

At least one image formation, usually the electron image, then has to be produced by oblique incidence, resulting in at least an undesirable distortion which has to be com- 3, l Patented Aug. 13, l 963 pensated yfor by some means. This again increases the complexity of the instrument and increases its weight and bulk. `One Way of overcoming this disadvantage would be to use a rnirror in front of the oil surface with a hole for the electron beam, but this produces the danger of Iundesired vignettin-g and unnecessarily lengthens the optical path.

For limited application in the field of telescopy, it is proposed, in Journal of the Optical Society of America, vol. 48, July 1958, page 500, to replace the oil with a thin, uniform, flexible, solid film` of low but finite electrical conductivity, having a reflecting coat of aluminum on one side and a mosaic of isolated targets on the other side, mounted over iaflat ring within a cathode ray tube equipped with a transparent window instead of the fusual screen. However, such a device, although providing a system in which electron and optical images are produced from or on opposite sides of the sensitive surface, still leaves room 'for considerable improvement in sensitivity, in the manner in which the visible light image is produced, in applications other than telescopy, and in numerous other factors.

Among the objects of this invention are to provide an improved device for the display of electron, X-ray, ultra- `violet, short wavelength, infrared images, or the like, or

vide such a device which may serve as an amplifier because it acts as a modulator in an optical projection system, thereby providing high power output and requiring a much lower input energy for the modulation; to provide such a device which includes a sensitive membrane which is resistant to shock and does not tend to be warped by excessive heat; to provide such a device which is not restricted to electron images produced by a scanning beam, i.e. those having a grid structure; and to provide such a device which may be utilized withrnumerous types of electron or image tubes.

Additional objects and the novel features of this'invention will become apparent from the description which follows, taken in connection with the accompanying drawings, in which:

FlfG. 1 is a condensedlongitudinal section of an image converter contructed in accordance with Vthis invention, utilizing Va phase contrast principle'for illumination and production of the im age; t

FIG. la is a vertical section along line lla-1a of FIG. l, showing a circular slit arrangement;

) FIG. 2 is a `diagram of theoptical system of the image converter of FIG. l, showing particularly the paths traveled by light rays;

FIG. 3 is a condensed, longitudinal section of an image converter` also constructed in accordance with this invention vand utilizing an interference principle for illumination and production of the image;

FIG. 4 is an enlarged section of a prism and associated membranes of the image converter of FIG. 3, also showing the paths traveled by light rays;

FIG. 5 is 4a fragmentary cross section, on an enlarged scale, of -an electroelastic membrane which may be used with the image converter of either FlG. l or FIG. 3.

PlG. 6 is a fragmentary cross section, similar to FIG.

5, of anotherform of elect-roelastic membrane, between Y which may be used with the membrane of either FIG. 1 or FIG. 3; and

FIG. is a diagram of an electron microscope which may be used in the systems of either FIGS. 1 or 3.

In accordance with this invention, an incident light, phase contrast system is utilized With'a modified image tube T of FIG. 1, attached to a housing H in which is installed the parts of the phase contrast im-age system. The

image tube T, having a housing 1l), as of glass, has been modified tofsubstitute for the conventional photosensitive screen a clear Window 11 and an electroelastic reflective membrane M, Whose construction is described slater, advjacent or supported by Window 11. The housing H, which may be formed of metal, as shown, such as aluminum may include transverse, intersecting rect-angular sections 12 and 13, generally in the form of :a T, with one end of section 12 receiving tube T and the opposite end integral `with or attached to the smaller end of a diverging section 14, in whose outer end is mounted a translucent screen l15. A light source 16 is mounted adjacent the outer end of housing section 13 and advantageously a suitable condensing lens 17 is mounted in a support 18 attached to the inside of section A13, to image the light source on a circular slit 19 in a plate 20 mounted forwardly of lens 17.

, Although only one lens 17 has been sho-wn, it fwill ber evident that any number of lenses may be provided to ac-y complish the desired result. Plate20 is opaque and thin,

while the center circular portion 2,1 of the plate may beV supported -by webs 21 which extend from the inner circular portion to the outer portion of the plate, these webs being very thin to prevent interference with the passage of 4light through the otherwise circular slit 19, or plate 20 may be transparent and the circular slit 19 produced by kproviding Vinner and outer opaque areas. Intermediate the lens 17 andthe slit 19 is a thin, transparent lilter 22, which carries an infrared reiiecting layer, such as magnesiumuoride. `Since the reflection of such an infrared filter depends on the angle between .the reilecting layer and the direction of light, this` angle is preferably adjusted so that the heat produced on the face of the electroelastic membrane M by absorption of infrared rays, which reach the membrane from the light source 16, is

Vequal to the` heat produced on the opposite side of the Ymembrane by electrons. As described later, an infrared lreflective coating is also provided on the -face of the membrane M, so that lwarping of the electroelastic membrane is avoided. Within'section 12 of housing H and opposite Ysection 13, a semitransparent mirror 23 is mounted in a bracket' 24, and :one or more lenses 25 and 2'6' are supported -in aligned relation by mounts 27, between mirror 23 and tube T. Although two lenses 25 and 26 are shown, it will :be understood that la single lens or any desired number of lenses may be utilized. At the opposite end v of section 12 is a transversely disposed plane glass plate 28, convenientll cemented to the inside of section 12 and on vWhich isfcentrally mounted -a phase ring'29', -Which is partially transparent and which is conveniently cemented to plate 28, or formed of lacquer. The thickness and ref.

fractive index of ring 29 are such that the phase of light passing through the phase ring is changed 180.

The end 31 of tube T opposite housing section 12 is conveniently formed of glass,` although it may be formed of metal, particularly when an electron image is pro- Vduced at cathode'32 by radiation entering endS-l, which projects electrons through an electron lens system to focus j the same on the rear side of membrane M. Cathode 32 preferably comp-rises a material which Will emit a steady, uniform stream of electrons, such as cesium, barium oxide or strontium oxide. The electron lens system comprises -a metallic cylinder 33, connected by means of a wireY 34 to ground or zero potential, a focusing ring 35, which'vis at a higher potential than cylinder .33.and is connected in the circuit .by means of a lwire 36, and a second cylinder 37, at a still higher potential and connected in the. circuit by means of a wire 38. The membrane is `absorbs part of the light.

connected to a high potential, on the order of 4,000' volts, by means of a lead 39, While each of wires 3,4, 36 and 38 and lead 39 are interconnected by a wire 40, with resistances 41, 42 and 43A of proper amounts to establish the desired potential between the cylinders and the focusing ring. Although thev value of 4000 volts is indicated in FIG. l, it will be understood that this value may bevaried, as will be apparent to one skilled in the art.. Y

The path followed by the light raysmay best be seen in the diagrammatic illustration of FIG. 2, in which a pair of light beam-s 45 and 46 pass through lens 17 and are directed through filter 22 and slot 19, which serves as the entrance pupil for the opticall system, represented by lenses 2S andl 26, Vthen against semitransparent mirror 23. Mirror 23 reliects part of the light, such as about 50%, so that it'pass'es through the optical system 25-26 and falls on the membrane M, such asfrepresented by rays 45a and 46a. If the membrane does 'not 'show any details or pro- 26 and reflecting membrane M. Because slit 19 was made f the entrance pupil, phase ring 29 is the exit pupil of the entire optical system. The phase ring 29 changes the phase of the direct'light that Vstrikes it by 180 and also The light rays 45C and'46c which pass through the phase ring, indicated bydotted lines, are projected upon the translucent screen 15, the image produced on the screen being viewed from the opposite thereof, in the arrangement shown.`

l The electron image 'emanatesfrom the cathoder32 to membrane M and as the electrons strike thetar'gets of the membrane, a distortion or profile on the membrane is prov duced, as will hereinafter appear. This electron image may `also be produced by a photo effect, such as X-ray,

ultraviolet, visible or near infrared rays. Since the membrane is thin, the distortionsor prolewill also appearron the opposite side of the membrane, causing any light which strikes its reilectivevsurface to be partially scattered.

Thus, -when membrane M shows details of a. profile, ypart of the light will be deviated by the profile and by-pass phase ringY 29, as indicated by rays 45d, 45e and 46d, 46e. Therefore, their phase and amplitude are not changed by phase ring 29. When the light through the phase ring and that Ib-y-.passing is united again at the screen 15, it will be intluenced by interference to produce darkness or partial darkness on those parts of the screen which correspond to points on the membrane with a prole. The

greater the profile, the greater the distortion and hence lmore light will be `dell-ected past ring` 29 to pass through plate 28 and increasethe brightness"ofthev image on `the screen 15. The relative brightness of the image and back' ground will thus change 'with the changein profile on thev membrane. Without "phaserring 29, the image projected upon screen 15 would be'phase modulated; however, the human eye can discern only an amplitude modulated image. Therefore, it i-s necessary to convert 'the phase modulated image to anv amplitude modulated, visible light image. The light need be deflected or scattered through a very small angle to causea significant change in the brightnessand contrast of the image projectedl upon screen KV15. Thus, the relief on the membrane need cnly'have a height of about one fourth of a wave lengthto be easily made visible. This is a considerable gain in sensitivity, as compared with the schlieren system. ,Although Vonly .one slit 19 and one phase ring 29 have been shown, a plurality of concentric phase ringsjand corresponding slits maybe provided, in order to increase the power of illumination.

The converter yalso acts as an amplifier, since a com-v paratively .small signal is chan-ged 'into an image of considerable brightness, through use of the high intensity light source V16. y,In addition, the use of the image converter is not restricted tothe lineftype of image, as produced by an electronic beam scanner, but can easily be Combined with the electro-optical image tube T.

Another image converter and `amplifier constructed in accordance with this invention is the interferometric or interference type, utilizing a Koester prism, as shown in FIG. 3, which may be arranged advantageously in a branched housing H', conveniently formed of aluminum or other suitable material. An image tube T', received in one end 48 of the housing H', is provided with a glass envelope 49', in which the Koester prism is conveniently enclosed. The Koester prism actually consists of two prisms 5i) and 51, abutting at an interface 52. Each prism is `a 60-3090 prism, preferably formed of quartz to prevent distortion of the prisms when heated, while separate membranes M and M are mounted in rings 53 and 54, attached to the base of the respective prisms 5G and 51, as by cementing. The membrane M' is activated from -a cathode 32', the electrons emanating from the cathode being focused on the membrane by an electron imaging system comprising cylinders 33' and 37' and a focusing ring 35', with `wires 34, 36, 38 and 4u, lead 39 and resistances 41, 42 and 43 serving the same purpose previously described. Light may be projected from a light source lr6, located in the outer end of an arm 55 of housing H', through a projection lens 56 securely mounted fon va support 57 within arm 55,` lens 56 causing the light rays from source 16 to be directed in parallel relation toward and perpendicular to the hypotenuse edge of prism 5G. While only one lens has been shown, it will be under-stood that a plurality of lenses may be provided, if desired. The end of envelope 49 adjacentV the Koester t prism conforms in shape thereto and light rays emanating from prism 51 will be directed through condensing lenses 53 and 59 held by mounts 6o in the inner end of a diverging arm 61 of housing H', in the outer end of which is mounted a translucent screen l5. v

As shown in FIG. 4, a light ray V62 from source 16 is directed against thel hypotenuse of prism 50, passing through the prism until it strikes the beam splitting inter- :face 52, which reflects one half 62a and the other half 62b passing into prism 51 each being reflected to the hypotenuse surface of the respect-ive prism and retracted onto the reflective surfaces of membranes M `and M". Only membrane M is affected by the electron image emanating from cathode 32', while membrane M'l serves to produce interference and thereby provide amplitude modulation to produce a visible image on screen' 15. Thus, the beams 62a and 62h will be reflected back from membranes M' kand M", as indicated by the double arrows on beams 62a and 6219, and if relief is formed on the membrane M lby the electron image emanating from cathode 32', the distance which must be traveled'by reilected lightbeam 62a will be shortened by an amount equal -to the height of the profile. Therefore, when the light beams are reilected back from the respective membran'es and recombined at the beam splitting interface 52, light beam 62a will be out of phase with light beam 62h, thereby causing a variance in the intensityof the light of the-combined light beam 62C, due to the interference between the reected light beams 62a and `6213. The light beam 62e will be projected through the `-lens system, including lenses 58 and 59, and the image will be Vfocused `upon screen observed from the exterior.

Thus, if `a relief has been formed upon' membrane M by an electron image, within the thickness of one fourth of a -wave length, interference betweenV the two lightbearns reflected from membranes M' land M" will produce the same light intensity variation or contrast as the contrast of the electronic image, after thetwo light beams are recomposed atV the interface 52. The interface 52 is normally provided with a beam splitting layer of platinum,

for other suitable material.

A second electron transmitter, affecting membrane M", can be built into the same tube. The second beam could alerter? material.

`be used either for superposition of two images, or for correction or adjustment purposes. If, for instance, the first beam plots an image of an -oscillographic curve, the second beam can' plot a coordinate system. The second beam can also be used for contrast control.

An advantage off the above arrangement, over the phase contrast system is that the former is symmetrical, a factor which helps to eliminate adverse influences. It is also a rigid body, Without any additional mechanical adjustment, except the fastening of the two membranes M' and M to the prism.

For the membranes, it is possible to use a comparatively thick membrane, as compared With the membrane proposed for use in the field of telescopy, and a piezo-electric or electro-strictive change in thickness of the membrane under the iniiuence of an electron charge on the sensitive surface of the membrane, with a positive voltage on the opposite, conductive side ofthe membrane. Such a layer is called here electro-elastic. The electro-strictive'or piezoelectric Iforces will then deform both surfaces equally, so that the opposite surface can be utilized without the necessity of light passing through the membrane. As in FIG. 5, the membrane may utilize the relief on the back side of a lperipherally supported membrane made of 'electro-elastic material 65, which may be a compact layer or powdered ferro-'electric material, such as barium titanate, suspended in a plastic or other suitable material. The mixture `can be poured into a plane-parallel layer by the thelp of two optically -plane ilats or other suitable plane surfaces, such as utilizing the appropriate surface of .a prism 5t) or 51, 'and polarized in an electrical field in a known manner. The ferro-electric particles must have a size comparable, or smaller than, an image point of the electronic image to be converted, but large enough to contain several domains, as known from the theory of ferro-electrics. Y

Theb'ack side of the layer 65 is coated with a highly reflective metal layer 66, to reliect the light from the light [source in eitherthe phase contrast or the inter ferometric systems. A mosaic layer 67 is then deposited on the up` per surface of layer 65, for instance, by sputtering or Avacuum deposition. The mosaic layer may be any pure metal, vbut can lalso be made of a photosensitive material,

Because it is important that the layer 65 be heated `equally on both sides in order to avoid warping, the vmetal reflective layer do on the back side of the membraneis coated with a thin layer of .infrared absorbing material 69, such as tinted glass, plastic, or other suitable layer is provided on' filter 22 of FIG. 1, vwhich is arranged between the light source 16 and the photo-elastic Ilayer 60 or membrane M. Since the reflection of such `an infrared iilterdepends upon the angle betweenthe layer and the `direction of the light, the angle is adjusted so that the j heat produced` o-n thefront side of the electro-elastic membrane by absorption of infrared rays is equal to the heat produced on' the back side of the membrane by the electrons. In this way, warping of the electro-'elastic membrane can be avoided.

An alternative membrane utilizing an internal phoitoi electric effect or photo conductivity may be used, as illus- As indicated above, an infrared reflecting v covered by a transparent conductive layer 74, such as a metal layer thin enough fto be transparent for the radiationto which the converter is sensitive. The other side of the electro-elastic layer 65' is covered with a metal reecting layer 66 which will carry a profile upon it, along with the electro-elastic layer when the latter is subjected to radiation, and serves to reflect the light from the projection system so that the relief formed by the electro-elastic layer will be made visible by either the phase contrast system or interference system. A D.C. voltage is applied between layers 66 and 74, as by leads 75 and 75 so that if the semi-conductive layer 73 s illuminated, it becomes conductiveto a certain depth and changes the electric eld strength through the photoelastic layer 65', which results in a change of thickness of layer `65 and a relief on the surface on-which the `reflective layer 66 is deposited. The reflective layer 66 then serves to relay the projected light beam from the converter, with the help of the relief formed upon Lthe layer, as explained above. The membrane may be attached to a support by means of the conductive layer 74,' provided the support is made'from a material which is transparent to the' radiation which is to be converted. It can, for instance, be directly attached to the surface of a kinescope, either on the outside whereby fthe radiation from the phosphor penetrates the glass senvelope,

t `r it canbe placed inside the picture tube, whereby the phosphorl can be directly deposited upon the conductive layer 74. .In thelatter instance, the projection system acts through the glass envelope in the reflection of the light beam.

A still further embodiment, as in FIG. 7, of a membrane utilizing a photo-conductive layer, includes a photoelastic layer 65 provided on opposite sides with two semi-conductivelayers 76 and 77. Semi-conductive layer 76 is photo-conductive, but while layer 77 need not be tube as shown in FIG. 8 may be utilized, including an `envelope #83 having an arm 84 in which an electron emitting cathode `85 is disposed. Anode 86 is'located forwardly of the sensitive conventer membrane M and collects electrons re-emitted from the photo-senstive mosaic layer 87 of the membrane. The radiation image to' be converted to avisible image is directed along a path indicated by arrows 88 and proceed through an image forming system, exemplified by lens 89. The tube of FIG. 8 may be substituted for the tube T of FIG. `1 or the tube T of FIG. 3. i

iA modulated cathode ray tub'e,"asin FIG. 9, may also be utilized in lieu of tube T of FIG. 'l or tube T of FIG. 3. The tube of FIG. 9 includesa flared envelope photo-conductive, it is convenientlymade of the same material. The layer 77 is covered with a non-conductive, reflection layer 78, as shown, or may be providedV with j an insulating layer covered with a metallic reflecting layer. Two equal DLC. voltages are applied across layers 76 and 77, as by leads 79, 79' and 80, 80', respectively. In addition, a D.C. voltage is applied between layers 76 and 77, as by leads 81 and 81', to produce a constant eld across `the electro-elastic membrane `65 as long as the photo-conductive layer 76 is not illuminated. As soon as the photo-conductive layer '76 becomes illuminated, however, the resistance of the layer in the illuminated Varea becomes smaller and thus the voltage drop over that area also becomes smaller. The field between layers 76 and 77vthus changes as a consequence and a relief is formed on the surface or surfaces of the electroelastic membrane-615, which can be made visible, `as

' explained above, by an optical projection system in which light is reflected from the reflecting layer 78.

The membrane of FIG. 7 is preferably used with a converter operating on the shadow-graph principle, as de- `scribed on page 565, Encyclopedia of Physics, vol.

XXIV, or on the Francon interference principle, as dev scribed in `Encyclopedia of Physics, vol. XXIV, page 640', both`of which are sensitive to fthe second derivativef a phase change in the projection image. 'This is necessary because the change of field between layers 76 and 77 is not a linear or approximately linear function of the Mintensity distribution in the image formed at the photo-V Iconductive layer 76 A projected image, using the shadow-graph or Francon method, would then be obtained inwhich the boundary line between areas of different contrasts is emphasized, i.e., the outlinesj of the image objects are clearer. This is motonly sufficient for many cases, but would often be an advantage, With such a membrane and projection system, it is of no consequence whether the image objects are lines or points,

-as in oscillographic displays or star images.

For 4producing an indirect electron image, a type of against a viewing screen.

90, in the larger end of which is disposed membrane M and in the smaller end of which is disposed a cathode 91, together with vertical deection plates 92 and horizontal deection plates 93. Y

A membrane M may also be used in the electron microscope tube of FIG. l0, having an elongated, flared, evacuated envelope 95, with membrane M disposed at the larger end thereof and a cathode 196 disposed in the opposite end, along with an electron optical condenser system 97, and an electron optical objective system 98.V The sample to be investigated is placed in a'container 99 between the condenser system 97 and objective system 98,

Vthrough the use of a vacuum lock arrangement. A n electron optical projective system may, if desired, be interposed between the objective systeml 97 and the membrane M. The tube of FIG. l0 may also be substituted for tube `T of FIG. l or tube T of FIG.' 3; Y

From the foregoing, it `will be evident that an image converter and amplifier constructed in accordance with this* invention fullls to a marked degree the requirements and objects hereinbefore set forth. Through the image plished vby means of an electroelastic membrane provided in an optical system, wherein an excitation image is directed against one side'of the electroelastic membrane, causing a 'distortion thereof so that visible light reflected from the opposite side of the membrane may be projected In the vembodiment of FIGS. l and 2, this is accomplished by using an optical system :wherein light is projected through aslit and forcused by means of a'lens system on the membrane. If thepme'm- -brane has been distorted so as to have ka profile, some of the rellected light will be scattered, the unscattered light passing through la phase ring, causing the phase of that light `to be changed by while the deflected or scattered light bypasses theiphase ring and combines with the u'nscattered light on the screen. This arrangement causes a phase modulated image, which would otherwise be produced,"to be converted to a visible, amplitude -modulated image on the screen.. Thus, it can be seen thatla change in the prole on the membrane causes an increase or `decrease in the amount of scattered light, resulting in a change in the brightness of the image and background projected on the screen.l This is a considerable gain in sensitivity, as compared with the Schlieren system. Also, in this embodiment a thin, transparent filter placed between the light source and membrane and carrying an infrared reilecting layer, may be angularly :adjusted with respect to the direction of the light, so that the heat produced on the face-of the electroelastic membrane,` by. absorption of infrared rays, may be made equal to the heat produced on the opposite sidejof the membrane byy the excitation beam, so that both sides' of thev membrane will be heated equally to,Y avoid warping,

Equally desirable results may be obtainedby the ,fuse

of lan interferometric or interference type system, utilizing a Koester prism, as in the embodiments of FIGS. 3

and'4. This system has an advantage ,overv the phase contrast system in Vthat it is symmetrical, helping to eliminate adverse influences. Also, the membrane is a 4rigid body, without any additional mechanical adjustment, except the fastening of the two membranes to the the prisms. iIn this embodiment, the light is split at the interface of the prisms and reected onto the membranes, then redirected back to the interfacewhere it is recombined and projected onto the viewing screen. A profile may be formed on one membrane, as by an electron image directed against the rear side thereof, to reflect the visible light rays, and cause a slight difference in the length of travel of the portion of the light beam directed against this membrane. Thus, the light beams will be out of phase when they recombine at the interface ofthe prisms, causing an amplitude modulation of the light which is projected against 'the screen. Thus, it can be seen that this optical system also converts an excitation image to a visible,` amplitude modulated image through interference of the refiected light beams. IFurthermore, in this embodiment, a second beam may be projected against membrane M for contrast, control or other purposes.

`It will further be apparent that the image converter and amplifier of both embodiments is not restricted to electron images produced by a scanning beam having a grid structure,.but may be used 'with numerous ltypes of electrons or image tubes. Also, the membrane used therewith is of relatively rugged construction which is resistant to shock, so that the device may be used under the most adverse conditions, such as for military purposes.

Although preferred embodiments of this invention have been illustrated and described, it will be understood that other embodiments may exist and Various changes and variations made, without departing from the spirit and scope of this invention.`

What is claimed is:

1. An image converter and amplifier comprising an electroelastic membrane adapted to form a relief corresponding to an excitation image; means for directing an image producing beam against one side of said membrane to form a corresponding relief thereon; a screen; a source of light rays; means for splitting said light rays and directing one portion of said light rays against the opposite side of said membrane, 4where said one portion is reflected, and directing another portion against said screen; means for directing said reflected portion against said screen; and means for combining said portions at said screen so that said relief causes interference between said `portions to produce an amplitude modulated image on said screen.

2. An image converter and amplifier as defined in claim l, where in said light splitting means comprises a semitransparent mirror.

3. An image converter and amplifier as defined in claim 2, including a plate provided with a slit and dis-` 5. An image converter and amplifier, -as defined in claim 3, wherein said plate is provided with a plurality :of concentric, circular slits and said partially transparent member has a plurality of .corresponding concentric, circular rings.

6. An image converter and amplifier as defined in claim 1, wherein said light splitting means lcomprises an .interface between a pair of abutting prisms.

7. An image converter and amplifier, as defined in claim 6, wherein said membrane is mounted on the base of one of said prisms.

*8. An image .converter and amplifier, as defined in claim 7, wherein a second and corresponding membrane is mounted on the base of the second prism.

9. An image converter Iand amplifier, as defined in claim l, including yan adjustable filter disposed in the path yof light from said light source, `said filter having an infrared refiectinglayer; and said membrane is provided with an infrared 'reflecting layer, said filter being adjustable to cause the amount of infrared rays received by said membrane to cause said lopposite yside of said membrane to be heated to the same extent as the side receiving said image producing beam.

10. AnV image converter and amplifier, as defined in claim 9, including means for adjusting said filter angularly with respect to the path of light rays from said source.

11. A n image converter and amplifier, as defined in claim 1, wherein lsaid image producing beam consists essentially of electrons.

12. An image converter and amplifier, as defined in claim 1, wherein said image producing beam includes X-rays.

13. An image converter and amplifier, as defined in claim 1, wherein said image producing beamV includes ultraviolet rays. l

14. An image converter and amplifier, as defined in claim 1, wherein said image producing beam includes infrared rays.

References Cited in the file of this patent UNITED STATES PATENTS Re. 22,734 Rosenthal Mar. 19, 1946 42,307,438 Whitaker Ian. 5, 1943 2,315,113 Farnsworth Mar. 30, 1943 2,330,171 Rosenthal Sept. 21, 1943 2,399,799 Guellich May 7, 1946 2,454,488 Sukurn-lyn NOV. 23, 1948 2,493,539 Law Ian. 3, 1950 2,510,846 Wikkenhauser .Tune 6, 1950 2,553,108 Osterberg May 15, 1951 2,718,811 Riepert Sept. ,27, 1955 2,727,170 Rudy Dec. 13, 1955 2,793,288 Pulvari May 21, 1957 2,896,507 Mast July 28, 1959 2,899,580 Dranetz etal. Aug. 1l, 1959 2,903,617 Turner Sept. 8, 1959 2,979,633 Harris Apr. 11, 1961 FOREIGN PATENTS 631,251 Great Britain Oct. 31, 1949 

1. AN IMAGE CONVERTER AND AMPLIFIER COMPRISING AN ELECTROELASTIC MEMBRANE ADAPTED TO FORM A RELIEF CORRESPONDING TO AN EXCITATION IMAGE; MEANS FOR DIRECTING AN IMAGE PRODUCING BEAM AGAINST ONE SIDE OF SAID MEMBRANE TO FORM A CORRESPONDING RELIEF THEREON; A SCREEN; A SOURCE OF LIGHT RAYS; MEANS FOR SPLITTING SAID LIGHT RAYS AND DIRECTING ONE PORTION OF SAID LIGHT RAYS AGAINST THE OPPOSITE SIDE OF SAID MEMBRANE, WHERE SAID ONE PORTION IS REFLECTED, AND DIRECTING ANOTHER PORTION AGAINST SAID SCREEN; MEANS FOR DIRECTING SAID REFLECTED PORTION AGAINST SAID SCREEN; AND MEANS FOR COMBINING SAID PORTIONS AT SAID SCREEN SO THAT SAID RELIEF CAUSES INTERFERENCE BETWEEN SAID PORTIONS TO PRODUCE AN AMPLITUDE MODULATED IMAGE ON SAID SCREEN. 